The invention relates to a piezoelectric valve with a one piece housing and a controllable sealing seat arranged within an elongated cavity in the housing. In particular, the valve employs an elongated piezoelectric bending element sealed off from and pushed into and held within the housing. The free end of the bending element closes or opens a sealing seat in accordance with an applied control current.
A piezo-ceramic bending converter is shown in EP-A1 0 191 011, in which the bending element is built into the housing in such a way that, at one end, it is supported at three points, of which one is adjustable and serves, at the same time, for contacting the middle electrode. The bending element is tightly connected and uses a separate guide spring which is connected to the housing and presses the bending element against the points of support. Using the free end of the bending element, an exhaust or intake air nozzle can be alternately closed or opened. The electric contacts for the piezoelectric bending element are brought out of the housing and sealed off.
The electrodes of the bending element and the contact pieces in the interior of the housing are not protected or insulated but are directly exposed to the streaming medium. As a result operation of the known arrangement with electrically conducting liquids is not possible. When a condensate forms, there is the danger of an electric short in the interior of the housing, and danger of corrosion at the points of contact. Since the points of contact are located in the interior of the housing, and are not separated from the work area, the electric contact points must be lead out of the housing in a gas-tight manner. The sealing-off between the bending element and the openings or nozzles to be controlled requires high-quality surfaces and exact inter-positioning, in order to achieve the lowest possible leakage values. The described conditions result in a relatively elaborate and costly manufacturing process as well as the additional disadvantage that the housing assembly is glued together and can only open by damaging it. Accordingly, the relatively expensive bending elements cannot be removed and reused after installation and adjustment.
A bending converter constructed as described above is shown in DE 44 10 153 C1, which suggests attaching an insulating cover layer onto the bending element. While this allows for the control of aggressive or electrically conducting liquids, the other described disadvantages remain.
Finally, WO 97/09555 shows a piezoelectric valve with a one piece housing having an lateral opening for receiving the bending element, which is cast permanently together with a casting material. Although the interior of the housing is sealed off, the device may not be dismantled without damaging or destroying the bending element. Furthermore, it is not insulated and thus has limited applications.